Prediction, interpretation and treatment of shear zones: A case study of an underground powerhouse cavern

摘要

The state-of-art technical developments in the engineering construction technology has made it now possible to implement any hydro power project, irrespective of its magnitude, wherein even geological setup of project is unfavorable & adverse. However, this poses immense challenge for the rightful selection of a suitable site for execution of huge underground excavation specifically in the heterogeneous rock conditions of Himalayan geology. The necessity of completion of project within the deadlines warrants the thorough geotechnical investigations to be conducted for avoiding geological surprise to the extent possible during the construction stage. Even detailed geological exploration carried out during investigation and pre-construction stage may not rule out presence of adverse geological features, as a fact of life. Underground power house cavern of Punatsangchhu-I H. E. Project encountered a major shear zone running across both the walls of the power house. This shear zone material was heterogeneous in nature and lost its strength in the presence of water. Managing such adverse geological feature often requires support of analytical approaches. Therefore, analytical analysis of power house cavern was carried out and shear zone treatment was evolved. Treatment included excavation of shear zone material up to a certain depth, plugging, rock bolting and shotcreting. This paper presents its prediction, interpretation & design aspects of power house cavern and methodology undertaken to treat the shear zone.